ActionScript3.0 一些觀念(三)

1.函數

函數語句定義法:
function testAdd(a:int, b:int):int{return a+b;}
函數運算式定義法:
var test:Function = function(a:int, b:int):int{return a+b;}

1.1函數預設參數
function test(a:int = 3,b:int=2,c:int=1):void
{
 trace(a+b+c,a,b,c);
}
test();//6,3,2,1
test(9);//12,9,2,1
test(2,9)//12,2,9,1

2.靜態屬性和方法
static var 屬性:屬性類型;
public static var 屬性:屬性類型 = 值;
static const 屬性:屬性類型 = 值; (常數就要先付予值)
static function 方法(參數):返回值類型{}
public static function 方法(參數):返回值類型{}

透過實例來存取靜態成員會出錯
var foo:StaticSample = new StaticSample(); // new了foo實例
trace(foo.CLASSNAME);
// 在StaticSample類別中有宣告一個靜態成員CLASSNAME
foo.hello();
//方法也是一樣

3.構造函數

package 
{
 import flash.display.Sprite;
 
 public class SampleConstructor extends Sprite
 {
  public function SampleConstructor()
  {
   var foo:Foo = new Foo();
   trace(foo);
   //輸出:[object Foo]
   var bar:Bar = new Bar("ActionScript3.0");
   //輸出Bar's counstructor!
   //init executed!
   //可以看出Bar一建立時，就執行了構造韓數中的語句
   trace(bar);
   //輸出:[object Bar]
   trace(bar.isOK);
   //輸出:ture
   //bar.isOK屬性在構造函數中成功初始化成true
   trace(bar.hello);
   //輸出:ActionScript3.0
  }
 }
}
class Foo()
{
 
}
class Bar
{
 public var isOK:Boolean;
 public var hello:String;
 public function Bar(hs:String)
 {
  trace("Bar's counstructor!");
  isOK = true;
  hello = hs;
  init();
 }
 function init():void
 {
  trace("init executed!");
 }
}

4.方法重載

package
{
 import flash.display.Sprite;
 public class SampleOverload extends Sprite
 {
  public function SampleOverload():void
  {
   overload();
   overload(3);
   overload("www.yahoo.com");
   overload(12,"123",new Object());
  }
 }
 private function overload(...args):*
 {
//(...args)寫法是說args變成一個陣列，每次值型丟進去的值
//都匯存進陣列中，在運用函式去分析
//:* 這意思是，丟進來怎樣類型的值，此函數經過處理後一樣return相同類型的值
  if(args.length == 0)return reportDefault();
  if(args.length == 1)
  {
   if(typeof(args[0])=="number")
   {
    return reportNumber(args[0]);
   }else{
    return reportErr(args[0]);
   }
  }
  if(args.length >1)return reportArray(args);
 }
 private function reportDefault():Boolean
 {
  trace("we got nothing");
  return false;
 }
 private function reportNumber(num:Number):Number
 {
  trace("we got number:"+num);
  return num;
 }
 private function reportErr(obj:*):*
 {
  trace("we don't understand this object:"+obj);
  return obj;
 }
 private function reportArray(ary:Array):Array
 {
  trace("we got an array :"+ary);
  return ary;
 }
}